1. Field of the Invention
This invention relates to a display control device capable of driving not only CRTs but also ELs, liquid crystal displays and other flat displays, using a CRT controller.
2. Description of the Related Art
When an EL, liquid crystal display, or other flat display is driven using a CRT controller, it is necessary to perform raster scanning at speeds twice those of CRT displays in order to prevent diminished screen brightness. Thus, when driving an EL or liquid crystal display using a CRT controller, single-scanning line signals are expanded into double-scanning line signals for output to the display. The LVIC design is one design for accomplishing this. This LVIC design involves retrieving display data equivalent to one screen from the data stored in a video memory and temporarily placing it into another memory, while simultaneously outputting double-scanning line signals from this latter memory to the display.
In the LVIC design, a single port RAM is used as the memory for storing display data for one screen. Data is read out for output to the display during times that display data is not being written into the RAM from the video memory.
Thus, since the conventional LVIC design requires reading out data for output to the display during times that display data is not being written into the single port RAM from the video memory, the timing of write operations to RAM and the timing of read out operations sometimes overlaps; in such cases, display data output is postponed When the bus occupation rate by write operations is high, the time available for output of data to the display is shortened, so the conventional LVIC design provides poor tracking with moving screens or when switching between screens, and experiences diminished brightness.